diff options
Diffstat (limited to 'compiler/codeGen')
| -rw-r--r-- | compiler/codeGen/StgCmmPrim.hs | 43 |
1 files changed, 43 insertions, 0 deletions
diff --git a/compiler/codeGen/StgCmmPrim.hs b/compiler/codeGen/StgCmmPrim.hs index 948af2aba0..8ec132b1d3 100644 --- a/compiler/codeGen/StgCmmPrim.hs +++ b/compiler/codeGen/StgCmmPrim.hs @@ -1746,8 +1746,51 @@ doCompareByteArraysOp res ba1 ba1_off ba2 ba2_off n = do dflags <- getDynFlags ba1_p <- assignTempE $ cmmOffsetExpr dflags (cmmOffsetB dflags ba1 (arrWordsHdrSize dflags)) ba1_off ba2_p <- assignTempE $ cmmOffsetExpr dflags (cmmOffsetB dflags ba2 (arrWordsHdrSize dflags)) ba2_off + + -- short-cut in case of equal pointers avoiding a costly + -- subroutine call to the memcmp(3) routine; the Cmm logic below + -- results in assembly code being generated for + -- + -- cmpPrefix10 :: ByteArray# -> ByteArray# -> Int# + -- cmpPrefix10 ba1 ba2 = compareByteArrays# ba1 0# ba2 0# 10# + -- + -- that looks like + -- + -- leaq 16(%r14),%rax + -- leaq 16(%rsi),%rbx + -- xorl %ecx,%ecx + -- cmpq %rbx,%rax + -- je l_ptr_eq + -- + -- ; NB: the common case (unequal pointers) falls-through + -- ; the conditional jump, and therefore matches the + -- ; usual static branch prediction convention of modern cpus + -- + -- subq $8,%rsp + -- movq %rbx,%rsi + -- movq %rax,%rdi + -- movl $10,%edx + -- xorl %eax,%eax + -- call memcmp + -- addq $8,%rsp + -- movslq %eax,%rax + -- movq %rax,%rcx + -- l_ptr_eq: + -- movq %rcx,%rbx + -- jmp *(%rbp) + + l_ptr_eq <- newBlockId + l_ptr_ne <- newBlockId + + emit (mkAssign (CmmLocal res) (zeroExpr dflags)) + emit (mkCbranch (cmmEqWord dflags ba1_p ba2_p) + l_ptr_eq l_ptr_ne (Just False)) + + emitLabel l_ptr_ne emitMemcmpCall res ba1_p ba2_p n 1 + emitLabel l_ptr_eq + -- ---------------------------------------------------------------------------- -- Copying byte arrays |